Rotational friction brakes are well known in the art. Examples of such brakes are disc brakes, drum brakes etc. They all have in common that they in one way or another subject a rotating body to pressure from one or more braking members on one of the surfaces of the rotating member, these surfaces being for example inside an enveloped surface of the rotating body, outside an enveloped surface of the rotating body, or on a plane side of the rotating body.
Most rotating friction brakes are operated by a system not in itself part of the rotating body, such as for example the braking system of a car or train. The braking power in these kinds of rotational friction brakes will thus not be regulated by the movement on the rotating body itself. There are also automatic rotational friction brakes, for which the braking power is dependent on the behavior of the rotating member. Examples of such brakes are centrifugal brakes. These typically consist of a plurality of braking arms connected to the rotating body such that said plurality of braking arms may be moved with respect to the rotating body along an axis that enables the center of gravity of the braking arm to move radially outwards as the angular speed of the rotating member increase. The braking power of these kinds of brakes thus depend on the angular speed of the rotating member.
In some applications, it may be beneficial to regulate a braking action based on the rate of change of the angular speed. Dependent on the situation, the braking action may occur for a positive rate of change of the angular speed, i.e. a (positive) angular acceleration, or a negative rate of change of the angular speed, i.e. a negative angular acceleration also referred to as an angular deceleration. There are several potential benefits of such a brake. An advantage is that it may be used for applications where high angular speeds are required. In such applications, centrifugal brakes are less suitable as they may considerably limit the rotational speeds.
A typical example of applications where this is a problem is systems such as e.g. cable drums, water hoses, large paper rolls and sewing thread rolls. These systems typically comprise a product (e.g. a cable, a hose, paper or thread) which is winded onto a spool at a plurality of revolutions.
An application where a positive rate of change of the angular speed may be used to actuate the brake is in the trolley system on elevators. In case of a malfunction wherein the elevator starts to accelerate downwards too fast, an angular brake actuated by positive angular acceleration may be allowed to activate thus reducing, or even stopping, the downward motion of the elevator already before a dangerous speed is reached.
An application where a negative rate of change of the angular speed may be used to actuate the brake is for fishing reels. The application is a typical example of a system where there is a need to promptly release a large quantity of a product from a spool, and that results in a considerable positive angular acceleration of the spool as the product is pulled from it. The phase of positive angular acceleration of the spool will end as soon as the pulling force on the product is zero. Unfortunately, the inertia of the spool will act to continue the unwinding, resulting in considerable risk of the product still contained on the spool to become entangled in itself, in the spool and in other mechanical parts in its vicinity.
A fishing reel comprises a frame and a line spool rotatably mounted in the frame. To prevent the spool during casting, from rotating at such a high speed that the line cannot be paid out at the same rate but instead rises forming a so-called birds nest (also called backlash), fishing reels are often equipped with a rotational braking system, usually comprising a combination of rotational brakes of different kinds, such as for example one or more friction brakes (e.g. centrifugal brakes, spool tension brakes etc.) and a magnetic brake. During a cast, the rotational speed of the line spool increases rapidly to maximum speed during a relatively short, initial phase of positive angular acceleration, to thereafter decrease during a longer phase of negative angular acceleration (deceleration).
Most rotational friction brakes of prior art, such as e.g. centrifugal brakes and magnetic brakes, are immediately actuated during a cast and thus produces a braking action commencing during the phase of positive angular acceleration. During this phase, there is however only a negligible risk of line rise, since it is the line, or more precisely the lure attached to it, that “pulls” the line spool, for which reason the line spool need not be subjected to braking during this phase. Braking the line spool during the phase of positive angular acceleration reduces the possibilities of making long casts. When the lure and the line are no longer “pulling” the line spool, i.e. during the phase of negative angular acceleration, it is however necessary to brake the line spool to prevent line rise.
Swedish patent SE506580 (granted 1998 Jan. 12 to Abu A B) discloses a brake system for fishing reels that aims to brake only during the phase of negative angular acceleration of the reel. This is achieved by using a plurality of braking arms where each arm is arranged to be in a non-braking position during a positive angular acceleration of the spool, and wherein each braking arm is arranged to flip over to a braking position during negative angular acceleration of the spool.
A particular problem with the invention disclosed in SE506580 is that the braking arms are positioned in a non-activated position during the whole phase of positive acceleration of the spool, and as the spool has reached its maximum speed, the braking arms flip into their activated position abruptly, initiating a quite significant braking of the drum as the braking power has a positive dependence on the spool angular velocity. Hence the braking action will not be smooth in the transition between a positive and a negative angular acceleration phase of the spool resulting in a reduced cast length and an undesired user experience.
Examples of such centrifugal brakes will now be provided for a clearer appreciation of the background art.
U.S. Pat. No. 3,587,474 A discloses a dragline winch for ski tows and the like, the dragline winch comprising a rotational friction brake having two brakeshoes 8 pivotally attached to a rotating body. The rotational friction brake of U.S. Pat. No. 3,587,474 A is actuated by the rotational speed of the rotating body through centrifugal forces.
U.S. Pat. No. 2,587,652 A discloses a braking mechanism for hose reeling apparatus. The braking mechanism comprises a pair of substantially semi-circular weights or brake elements pivotally mounted on an inner rotating drum. The braking mechanism is disclosed as a centrifugal braking mechanism which is thus actuated by the rotational speed of the rotating body through centrifugal forces.
U.S. Pat. No. 2,055,358 discloses a fishing reel comprising a rotational friction brake having a plurality of brake members disposed and provided with pivotal connections intermediate their ends upon the rotatable wall of the shield. The rotational friction brake of U.S. Pat. No. 2,055,358 is centrifugally operated, i.e. actuated by the rotational speed of the rotating body through centrifugal forces.
U.S. Pat. No. 6,076,640 discloses fishing reel comprising a rotational friction brake having a pair of brake levers which are biased in a braked position using bias springs. The brake levers are pivotally connected to a lever base arranged to rotate with the spool. One portion of the brake levers, the counter weight arm, is equipped with a counter weight whereas another portion of the brake levers, the braking lever, is arranged to frictionally engage a non-rotating outer body, a brake drum. The rotational friction brake of U.S. Pat. No. 6,076,640 is centrifugally operated, i.e. actuated by the rotational speed of the rotating body through centrifugal forces.
U.S. Pat. No. 3,477,659 A discloses a rotatable spool fishing reel comprising a friction brake acting between the casing and the spool wherein the friction brake comprises one or more brake shoes arranged to frictionally engage the casing. The rotational friction brake of U.S. Pat. No. 3,477,659 A is urged into engagement by the effect of a centrifugal force, i.e. actuated by the rotational speed of the rotating body through centrifugal forces.